A conventional fixing device employed for an electrophotographic type image forming device includes a circularly movable tubular fusing belt having an inner peripheral surface defining an internal space, a halogen lamp disposed within the internal space, a pressing pad with which the inner peripheral surface of the fusing belt is in sliding contact, and a pressure roller for nipping the fusing belt in cooperation with the pressing pad. The halogen lamp is provided with a glass tube and a filament as a heat source. The filament is sealed in the glass tube with sealed portions formed at both ends of the glass tube.